Assistive Listening Knowledge Base
  • Peer-reviewed study

On the importance of early reflections for speech in rooms

From https://assistivelisteningknowledgebase.org/evidence/bradley-2003/ · record checked 13 October 2026

  • Bradley JS, Sato H, Picard M
  • Journal of the Acoustical Society of America 113(6):3233-3244

Independent (National Research Council Canada; Université de Montréal)

Summary

Speech intelligibility tests in simulated sound fields and analysis of measured room responses on the role of early reflections.

Key findings

  • Adding early reflections, arriving within 50 ms of the direct sound, increased the effective signal-to-noise ratio and intelligibility scores as much as an equal increase in direct-sound energy.
  • The benefit held both for younger listeners with near-normal hearing and for older listeners with mild to moderate high-frequency hearing loss; none of the 21 listeners in the initial tests used hearing aids.
  • In measured rooms for speech, early reflections raised the effective signal-to-noise ratio by up to 9 dB, most at seats far from the talker.
  • Section II.B.2 divides the 21 participants in the initial tests into 11 with near-normal hearing and 10 with greater hearing loss; the latter needed approximately 5 dB higher SNR for similar intelligibility in this experiment. This is a group result, not a universal target. Separate study funding is not stated in the archived manuscript.
  • Section II.B.3 uses a partly different sample of 16 listeners (10 with near-normal hearing and six with greater hearing loss) for the tests with added late reverberation. The initial 21-person sample is not a total for every experiment in the paper.

Limits

Simulated sound fields in an anechoic room; reflections of a single source, not two separate systems carrying the same programme; no listeners with severe hearing loss, which the authors say still needs testing.

Read the original

nrc-publications.canada.ca/eng/view/accepted/?id=dd3c1e7a-8d8d-440e-bbcd-04c69ef20419

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Cited in

Cite this source

Bradley JS, Sato H, Picard M. On the importance of early reflections for speech in rooms. Journal of the Acoustical Society of America 113(6):3233-3244. June 2003. https://nrc-publications.canada.ca/eng/view/accepted/?id=dd3c1e7a-8d8d-440e-bbcd-04c69ef20419 (accessed 13 October 2026).

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